1. Field of Endeavor
The present invention relates to stable, concentrated, aqueous and water-soluble fertilizer suspensions formulated to provide plant nutrition for growing plants, and more particularly to stable, concentrated, aqueous and water-soluble suspensions of mineral salts and nutrient additives.
2. Description of the State of the Art
For healthy and rapid growth, particularly in a hydroponic environment, plants require a nutritionally balanced soluble nutrient feed program. Some liquid mineral fertilizers comprising mineral salts have limited solubility in water. Additionally, some of the elements required for plant growth form insoluble compounds at low concentration levels that precipitate. Liquid fertilizers typically contain the major macronutrients of nitrogen, phosphorous, and potash and the micronutrients: iron, manganese, zinc, copper, boron, molybdenum and frequently omit the intermediate elements of calcium, magnesium, and sulphur. When using liquid fertilizers of this type, one can experience imbalanced growth and nutrient deficiencies in the plant. Liquid fertilizers may be accumulated to provide complete plant nutrition for growing plants. For example, in order to achieve a complete nutrient profile, the feed program may include at least two nutrient containers of ionic nutrients to avoid or minimize precipitation of ions prior to their application to the target hydroponic culture. A well known formulation for solutions in which plants may be grown in hydroponic cultures is Hoagland's solution where a first solution includes potassium nitrate, calcium nitrate, monopatassium phosphate, magnesium sulfate, an iron chelate, and a second solution is a micronutrient stock solution that includes boric acid, manganese chloride, zinc sulfate, copper sulfate and molybdic acid. In addition, Hoagland's solution may achieve a lower pH by the application of ammonium. To apply the Hoagland's solution, this two-solution or two-container approach requires that, in order to provide a complete nutrient feed, one must mix two separate concentrates and dilute each in a user solution to avoid precipitation. From a commercial distribution perspective, one may have to ship sufficient water along with the concentrate in that the water increases handling costs over just the necessary feed.
As an alternative to aqueous suspensions, dry nutrient blends may not contain the full gamut of minerals of a complete solution, and dry nutrient blends may not be completely water-soluble. In hydroponic systems having nutrient monitoring, the effects of the application of a dry nutrient blend to the hydroponic culture may be measurable and affect the subsequent frequency and amounts of the dry nutrient blend that may be added. If the dry nutrient blend is to be dissolved in hydroponic culture comprising cold water, several minutes or several hours may be required to achieve a complete dissolution. This cold water delay injects a non-negligible delay between recognizing the need for an application of a solution feed and actually delivering the solution feed. Likewise in bulk applications of the dissolved dry nutrient blend from a dilution container, several minutes or several hours may be required prior to administering to plants. Furthermore, many dry formulations that contain all the nutrients generally recognized for plant growth are hygroscopic, and absorb moisture from the atmosphere, and may eventually turn an original dry formulation exposed to atmospheric moisture into a sticky paste or one or more solid chunks that may be impractical to measure and dissolve. In addition, a complete dry nutrient blend may be mixed with water to form a liquid suspension and stored in a sealed container which may not exhibit sufficient shelf life. For example, an adverse gaseous chemical reaction may set up over several days that can cause the sealed container to swell, rupture, and leak a brine solution. Thus, a complete dry nutrient blend may be mixed with water to form a liquid suspension, but may be unstable and unsuitable for manufacturing and packaging in sealed storage containers.
Aqueous fertilizer suspensions producing particles that may settle out while on the shelf include the teachings of U.S. Pat. Nos. 3,519,413, and 3,950,159, both of which disclose a suspension of coarse particles and a hydrophilic or a polysaccharide gum for thickening. U.S. Pat. No. 4,069,034 describes a method of making a suspension fertilizer with bentonite and humic acid as crystal growth modifiers. The teachings of this disclosure are directed to a manufacturing process that deals with supersaturating nitrogen and phosphorous in a reactor at elevated temperatures. U.S. Pat. No. 4,525,197 discloses a fertilizer suspension that utilizes magnesium-aluminum silicate as a stabilizer along with a dispersant selected from sorbitol, polyvinyl alcohol, caseinate, and soluble starch hydrolosates to prevent the formation of large crystals. U.S. Pat. No. 5,851,260 discloses a suspension fertilizer suitable for irrigation fertilization and a process for its preparation, and its teachings to not appear directed to a complete fertilizer, having exemplary solutions made from relatively inexpensive, i.e., field grade, fertilizer raw materials with known water insoluble compounds not readily applicable to hydroponic cultivation. U.S. Pat. No. 5,997,602 discloses a method of manufacturing an aqueous fertilizer suspension containing at least phosphate, and calcium and magnesium ions, and its teachings appear to address suspensions that may or may not be nutritionally complete, and producing an inexpensive, i.e., field grade, fertilizer with insoluble material acceptable for a drip irrigation in field use, and where the exemplary form of nitrogen taught is urea. Because water-soluble mineral nutrients are derived from mineral salts, there is an equilibrium point for these salts to form crystals and for the crystals to slowly dissolve back into solution. Because large crystals form at the expense of smaller ones, i.e. Ostwald Ripening, there is a progressive tendency to grow water-soluble crystals in the concentrate. Such water-soluble crystals may eventually grow quite large and sink to the bottom of the suspension. These are particularly troublesome with mineral salts that have a wide range of solubility over different temperatures. This is particularly troublesome with potassium nitrate and urea.
A technique in the formulating arts is to use a cosolvent that is miscible with the solvent that lowers the solubility of the mineral salt and slows the rate of crystal growth. The problem is that few cosolvents are non toxic to plant growth. Another technique to overcome this is to create a non-aqueous suspension as disclosed in U.S. Pat. Nos. 5,707,551, 5,906,962, and 6,743,756 and as described in US Patent Application No. 2002/0065198 A1. U.S. Pat. No. 5,707,551 describes non-aqueous suspension concentrates of highly water-soluble solids where the liquid composition is completely non-aqueous and also requires a complex three-component surfactant system. U.S. Pat. No. 5,834,533 describes stable suspension compositions where the liquid composition is non-aqueous and the application is directed toward well drilling fluids. U.S. Pat. No. 5,906,962 discloses a method of non-aqueous suspension concentrates of highly water-soluble solids. U.S. Pat. No. 5,906,962 is a continuation-in-part of U.S. Pat. No. 5,707,551 based on a non-aqueous solvent and a complex three-component surfactant system, and appears directed toward suspending a slightly water-soluble active compound, e.g., pesticide or herbicide, with a water solubility of less than 1%. U.S. Pat. No. 5,925,182 describes stable liquid suspension compositions, some having limited solubility; a non-aqueous liquid suspension appearing to be directed toward well drilling fluids. U.S. Pat. No. 5,969,012 discloses non-aqueous slurries of water-soluble polymers, where the solvent is non-aqueous and is a vehicle for concentrated water-soluble polymers. U.S. Pat. No. 6,743,756 describes suspensions of particles in non-aqueous solvents, and appears to be directed toward the use of a castor wax as a stabilizer.